When a valve seat member is pressed into a bore in a fluid passageway of a valve body, it is a typical practice to provide the valve seat member with a lead-in that serves to align the valve seat member with the bore for a proper press fit. The lead-in is required to have a certain chamfer angle so that metal is properly displaced during the press-fitting operation.
The constraints imposed on certain valves may be such that a valve seat member can be pressed into a valve body bore from only one direction, and there may be impediments to obtaining a proper press-fit. One such impediment may involve the nature of the bore itself. The bore may have a counterbore through which the valve seat member must pass before it reaches the press-fit diameter portion of the bore. This provides a potential for a greater degree of misalignment between the seat member and the press-fit diameter portion of the bore during the process of inserting the seat member into the bore. Certain constraints are also imposed on the lead-in, especially as it merges into the press-fit diameter portion of the seat member. Typically, the chamfer angle of the lead-in must be rather shallow as it merges into the press-fit diameter portion of the valve seat member, fifteen degrees for example. Also, the fifteen degree chamfer must have an axial dimension that will assure a proper radial distance of its beginning relative to the press-fit diameter portion of the seat member. When a seat member is pressed into a valve body bore by automated assembly equipment, some degree of alignment must be inherent in the equipment; yet, this may not always be sufficient for certain valve designs. A more precise alignment may be helpful, but it may be rather expensive and it may not always provide a desired degree of improvement.
Given constraints and considerations such as those just discussed, it may happen in the automated assembly of valve seats into valve body bores that an occasional misaligned valve seat member nicks a shoulder of a counterbore as it is being inserted into the bore, shaving a sliver of metal in the process. This could affect the press fit, or even separate.
The present invention is directed to a novel construction for a lead-in that results in improved press-fitting of a valve seat member to a bore of a valve body. While some degree of improvement in accuracy of assembly equipment may be helpful, it is believed that the present invention provides sufficient improvement in its own right that it may be a more efficient way to improve the press-fitting process so that there is a significantly reduced, if not entirely eliminated, potential for nicking of a counterbore with potentially attendant silver generation.
The present invention contemplates the provision of a lead-in that has two distinctive regions: one, an initial chamfer portion that is has angle and size which assure that at maximum misalignment and all lesser degrees of misalignment, it will engage the counterbore shoulder without shaving material from the bore at the junction of the shoulder and the press-fit diameter portion of the bore; and two, a transition chamfer portion that provides a transition between the initial chamfer portion and the press-fit diameter portion of the valve seat member. The transition chamfer portion has a chamfer angle less than the chamfer angle of the initial chamfer portion that assures that the transition chamfer portion also will not shave material from said bore at the junction of the shoulder and the press-fit diameter portion of the bore.
In the disclosed embodiment, the angle of the initial chamfer portion is substantially 30 degrees and that of the transition chamfer portion is substantially 15 degrees. The initial chamfer portion and the transition chamfer portion meet at a radial distance from the press-fit diameter portion of the valve seat member that is 0.050 mm.
The foregoing, as well as further features, advantages, and benefits of the invention will be seen in the ensuring description and claims which are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.